In automated testing of printed circuit boards it is necessary to align the printed circuit board with the probes of the test fixture. Conventionally this may be done by means of alignment holes in the printed circuit board which are adapted to be aligned with alignment pins carried by the fixture.
Prior art printed circuit board fixtures have used alignment pins which are of uniform diameter along their length and have a fixed length. The diameter of the alignment pins must be closely sized to the diameter of the alignment holes in the printed circuit board to ensure proper positioning of the board for testing. This is necessary because the probes of the testing unit must contact the proper electronic devices and electrical contacts on the board in order for reliable testing to be conducted.
However, exact positioning of the board is not possible due to clearances between the alignment holes in the printed circuit board and alignment pins in the test fixture. These clearances must exist due to manufacturing tolerances in the diameter and position of the alignment holes in the printed circuit board and alignment pins in the test fixture.
If tolerances are not held closely this requires that the alignment pins be undersized, and therefore the printed circuit board is not held in proper alignment and can shift from the ideal position. If the alignment pins are oversized the printed circuit board may bind on the alignment pins. As a result, the printed circuit board cannot be placed into proper position for testing.
Thus, it has been necessary to maintain proper selection of alignment pins, and also maintain proper tolerances, to assure that a printed circuit board is properly aligned in the fixture for desired testing.